Apple has launched an internal investigation into damning reports alleging that its supplier Quanta Computer illegally employed high school students to assemble Apple Watch units in China’s Chongqing, reportedly pushing employees to work overtime and night shifts.

Here’s what Apple said in response to these allegations:

We are urgently investigating the report that student interns added in September are working overtime and night shifts. We have zero tolerance for failure to comply with our standards and we ensure swift action and appropriate remediation if we discover supplier code violations.

Monday’s report by The Financial Times said that Students and Scholars Against Corporate Misbehavior (Sacom), a Hong Kong-based labor rights group, had discovered this after interviewing 28 such students this summer at a Quanta manufacturing plant in Chongqing.

From the report:

Students said they were sent to the factory by their teachers for ‘internships’, but performed the same jobs as other assembly line workers and often worked overtime and night shifts, both of which are illegal for student interns under Chinese law.

Eleven students said their teachers told them they would not graduate on time if they did not complete the internships. All 28 students said they worked overtime and night shifts.

One student told Sacam they were scheduled to work night shits from 8pm to 8am with only one day off per week, while another described the repetitiveness of the job by saying: “We repeat the same procedure for hundreds and thousands of times every day, like a robot”.

It is not uncommon for local governments in China to actively encourage schools to supply local factories, hoping doing so might attract investment to the area. In an earlier investigation, Sacom had unearthed similar labour abuses at Quanta’s Chongqing plant, but Apple denied that the facility was a part of its supply chain (which may have been true at the time).

This isn’t the first time Apple’s Asian suppliers were targeted by Sacom.

Last year, for example, Secom found that student interns had illegally worked overtime at Foxconn’s iPhone plant in Zhengzhou, prompting the company to end the practice.

Other reports likening these plants to sweatshops were published in 2011 and 2012.